With the progress of post-genomic science, information has accumulated about the structures and functions of biomolecules such as proteins or RNAs. There has been a growing tendency of synthetic biology, which exploits such increasing information to understand the systems of life through “synthesis”, in contrast to previous reductive or analytical biology. Particularly, the artificial (re)construction of biomolecules or genetic circuits has received considerable attention in terms of not only life science research but also industrial application. Particularly, there has been a demand for the progress of translational regulatory systems which can recognize a particular protein and regulate arbitrary gene expression.
Heretofore, the conventional technique is known, in which the induction of transcription of DNA is regulated by small molecules or proteins (see Non-Patent Document 1). This technique is a method for modulating the regulation of transcription from DNAs to RNAs. However, this technique had the problem that it cannot be applied directly as a technique of regulating translation from RNAs to proteins. Moreover, there is a naturally occurring system (S15, ThrRS, etc.) in which the protein regulates a translation level upon binding to its own mRNA 5′ untranslated region (5′-UTR). However, no artificial translational repression/activation system of a target gene using such an RNP interacting motif has been constructed intracellularly or extracellularly.
Moreover, RNAs called “riboswitches”, in which mRNAs induce structural change in response to metabolites, resulting in the regulation of gene expression, have been discovered in recent years in bacteria and have received attention. However, natural riboswitches use substrates limited to small molecules such as vitamins or amino acids and therefore, cannot regulate gene expression in response to biomacromolecules such as RNAs or proteins. Furthermore, natural riboswitches are limited to systems for performing the feedback regulation of their own expressions and therefore, have not been applied so far to the development of artificial systems that regulate arbitrary gene expression. Thus, the development of artificial riboswitches having such functions has been expected.
The conventional technique is known as to translational regulation using RNA aptamers or antisense. There also exists a technique which involves introducing a small molecule theophylline-binding aptamer into an artificial RNA using yeast to prepare an “RNA switch” which performs ON/OFF regulation of gene expression in a manner dependent on the presence of theophylline (Non-Patent Document 2). However, this technique had the problem that it is a system responding to the aptamer for small molecules and therefore, cannot be applied to biomacromolecules such as proteins as substrates.    Non-Patent Document 1: Trends Biochem Sci. 2005; 30 (6): 275-9    Non-Patent Document 2: Nat Biotechnol. 2004 22 (7): 841-7. 2004